Coded data generation or conversion – Analog to or from digital conversion – Differential encoder and/or decoder
Patent
1997-01-09
1998-11-10
Hoff, Marc S.
Coded data generation or conversion
Analog to or from digital conversion
Differential encoder and/or decoder
341 77, H03M 302
Patent
active
058350411
DESCRIPTION:
BRIEF SUMMARY
This application is the U.S. national-phase application of PCT International Application No. PCT/EP95/00805.
BACKGROUND OF THE INVENTION
The present invention relates to a circuit for conditioning and digitizing an analog signal and includes a trigger circuit which processes the analog signal by way of a variable hysteresis which adapts to the signal to be conditioned. The present invention also relates to a circuit for signal conditioning and digitizing.
DE 39 36 831 A1 discloses a circuit for conditioning the analog output signal of a rotational speed sensor which includes a trigger circuit with controllable change-over points or "hysteresis". The coupling factor is determined and multiplied by the frequency of the sensor signal that corresponds to the rotational speed to produce the amplitude of the sensor output signal. The hysteresis of the trigger circuit is then varied as a function of the coupling factor or adapted to the coupling factor. The hysteresis increases with a high coupling factor and decreases with a low coupling factor. The precise calculation of coupling factors in the initial period of a rotation and at rising rotation angular velocity adds to the cost of the circuit.
For example, circuits of this type are required for evaluating the wheel sensor signals which furnish the data needed for control in vehicles having brake systems with anti-lock control or traction slip control. In conventional passive transducers or wheel sensors, the measuring signal is greatly dependent on the wheel speed and the air slot between the transducer and the toothed disc which rotates with the wheel and produces the signals in the transducer by induction. Especially at a low rotational speed and with unfavorable manufacturing tolerances, for example, when a large air slot exists due to tolerances, there is the risk that the useful signal is difficult to distinguish from inevitable spurious signals. Therefore, additional effort is expended during manufacture and assembly to improve manufacturing tolerances.
SUMMARY OF THE INVENTION
An object of the present invention is to improve the interference protection during acquisition of the analog signals, such as acquisition of the previously described measuring signals by way of wheel sensors, and to reduce the expenditure for circuitry, particularly for analog signal processing circuitry. The output signal of the circuit to be configured should be compatible with the present methods and circuits for signal processing and signal evaluation.
This object can be achieved by a circuit of the previously mentioned type which involves, in particular, a control circuit taking the form of a delta modulator that has a comparator which compares the analog signal to be conditioned (which is the reference input of the control circuit) with an adapted signal. The comparator produces a binary signal representative of the signal variation and conducts it to a clock-controlled bistable flip-flop. The output signal of the bistable flip-flop is a binary data stream representative of the difference between the signal to be conditioned and the adapted signal. The data stream is integrated in a digital accumulator and, by way of a digital-to-analog converter, is conducted as an adapted signal to the second input of the comparator. The integration time constant, or the numerical value that is respectively added in the accumulator in the integration cycle, is variable as a function of the output signal of the flip-flop. The digital output signal of the accumulator is evaluated by a digital threshold value comparator which compares the digital output signal, in consideration of the sign, with the mean value of the quantity of the digital output signal, to produce a conditioned square wave signal corresponding to the analog input signal.
According to the present invention, the analog input signal is processed using principles and methods of digital signal processing. By employing a control circuit known as delta modulator, a digital signal is produced which is then evaluated by means
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Fey Wolfgang
Traskov Adrian
Zydek Michael
Hoff Marc S.
ITT Automotive Europe GmbH
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